A torque converter as a fluid type power transmission device is embedded with a lock-up device in order to reduce fuel consumption. The lock-up device is disposed in a space produced between a turbine and a front cover, and is configured to mechanically couple the front cover and the turbine in order to directly transmitting torque therebetween.
In general, the lock-up device includes a piston and a damper mechanism. The piston is pressed onto the front cover by the action of hydraulic pressure, and torque is transmitted to the piston from the front cover. On the other hand, the damper mechanism includes: an output-side member coupled to the turbine; and a plurality of torsion springs for elastically coupling the piston and the output-side member. Moreover, the torque transmitted to the piston is transmitted to the output-side member through the plurality of torsion springs, and is further transmitted to the turbine.
Incidentally, PTL 1 describes a lock-up device that an inertia member is attached to the output-side member in order to inhibit variation in engine rotation. In the lock-up device described in PTL 1, the inertia member is attached to the output member fixed to the turbine, while being rotatable relatively thereto. Further, torsion springs are disposed as elastic members between the output member and the inertia member.
In the lock-up device of PTL 1, the inertia member is coupled to the output member through the torsion springs. Therefore, the inertia member and the torsion springs function as a dynamic damper, and these components attenuate variation in rotational speed of the output-side member (turbine).